Heat treatment of powder compacted components is undergoing constant development in line with development on traditional, solid materials.
Consequently, the processes used are the same as those used on solid steel, and the purpose of heat treatment is usually the same as is the case with solid steel.
This might, for instance, be to increase strength, hardness, wear resistance or corrosion resistance.
At Dansk Sintermetal A/S we primarily use the following heat treatment methods.
Neutral hardening, which is carried out on components with relatively high carbon content, typically 0.6% C. Components are core hardened and acquire strength and hardness. As a result of core hardening relatively large changes in dimensions are to be expected.
Carbonitriding is typically performed on components with a carbon content of approx. 0.2% C. To avoid process gases penetrating the porous system – which would result in the core hardening of the components – efforts are made to have high density components. Alternatively, the pore system can be closed with steam treatment.
Carbonitriding is performed briefly and at low temperatures, with only limited dimensional changes as a result.
The finished components are extremely strong, have high surface hardness and good tribological properties when used together with many other materials.
After carbonitriding hardness should normally measure at HV0.2 or HV0.1 to avoid penetration of the thin hardened layer during hardness tests.
Nitrocarburizing is also typically performed on components with a carbon content of 0.2% C. As in the case with carbonitriding this involves a gaseous process, the same conditions apply with regard to the closing of the pore system. In the case of nitrocarburizing an extremely thin (typically 10-20µm) hard connection zone of iron nitrides with small amounts of dissolved graphite is formed. This connection zone gives the components particularly good wear characteristics, whilst the underlying diffusion zone provides improved fatigue strength.
Often nitrocarburizing is combined with an integrated oxydising, which considerably increases corrosion resistance.
The processing temperature is usually only 570 °C and changes in shape are therefore minimal.
After nitrocarburizing hardness should normally be measured at HV0.1 to avoid penetration of the thin hardened layer during hardness tests.